One of the leading reasons for a root canal treatment is that the pulp tissue gets exposed to bacteria. The enamel and dentin in a healthy tooth is there to protect this very sensitive core of your tooth. However if you suffer from cavities, and have a hole in your teeth, the bacteria might eat into the rest of your teeth and quickly expose the center of your teeth.
Injuries from accidents and other sports activities can also lead to trauma caused by damage to the pulp tissue, in this case it is advised that you quickly get proper treatment done. Sometimes, having multiple crowning and filling procedures done to the same tooth may also lead to pulp tissue exposure.